<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style>
    .container {
      height: 1em;
    }
    .overflow {
      height: 8em;
    }
    body {
      font-family: monospace;
      height: 8em;
      line-height: 1em;
      -moz-column-count: 2;
      -moz-column-gap: 0;
    }
</style>
<script>
    function boom()
    {
      document.documentElement.offsetHeight;
      document.getElementById('x').style.display = 'none';
      document.documentElement.offsetHeight;
      document.getElementById('y').style.display = 'none';
    }
</script>
</head>

<body style="width: 17ch;" onload="boom();"><div id="x" class="container"></div>This paragraph must be in the first column.<div class="container" id="y"><div class="overflow"></div></div></body>
</html>
